Moduli Fixing in Realistic String Vacua

TL;DR

This paper demonstrates the existence of heterotic-string models where all moduli are projected out, challenging the traditional geometric interpretation of extra dimensions in string theory.

Contribution

It introduces specific Z2 x Z2 orbifold models with asymmetric projections that eliminate all untwisted and twisted moduli, offering a new perspective on extra dimensions.

Findings

All moduli can be projected out in certain heterotic-string models.

The models are based on Z2 x Z2 orbifolds with asymmetric projections.

Extra dimensions may not have a physical realization in these models.

Abstract

I illustrate the existence of quasi-realistic heterotic-string models in which all the untwisted Kaehler and complex structure moduli, as well as all of the twisted sectors moduli, are projected out by the generalized GSO projections. I discuss the conditions and characteristics of the models that produce this result. The existence of such models offers a novel perspective on the realization of extra dimensions in string theory. In this view, while the geometrical picture provides a useful mean to classify string vacua, in the phenomenologically viable cases there is no physical realization of extra dimensions. The models under consideration correspond to Z2 X Z2 orbifolds of six dimensional tori, plus additional identifications by internal shifts and twists. The special property of the Z2 X Z2 orbifold is that it may act on the compactified dimensions as real, rather than complex, dimensions. This property enables an asymmetric projection on all six internal coordinates, which enables the projection of all the untwisted Kaehler and complex structure moduli.